Why am I expected to invite relatives I don't know or strongly dislike to our wedding?

My mom was really upset when I told her that my grandma's (her mother who's been passed away for about 7 years now) extended family wasn't invited. She expects me to invite my aunt's (her sister-in-law) step mother and step sister who have hosted Thanksgiving dinner the past few years for our... show more My mom was really upset when I told her that my grandma's (her mother who's been passed away for about 7 years now) extended family wasn't invited. She expects me to invite my aunt's (her sister-in-law) step mother and step sister who have hosted Thanksgiving dinner the past few years for our families (She doesn't know that I'm not inviting them either), and I have no choice but to invite that actual aunt because she's married to my uncle (mom's brother) who I actually adore. His wife (my aunt...in case this is hard to follow) is a very mean person. She always goes out of her way to upset my mom and she always liked to compare me to her daughter who's a year older than me. She thinks her kids are so far above us that we aren't worthy of their friendship as cousins. She's a loony toon. I mean the woman suffered from empty nest syndrome and filled the void by buying 3 Chippewas that she calls her latin gang. The dogs all fit in my hand. My uncle hates them, and he's a dog person! My aunt never respects my uncle. She used to have 2 cats even though my uncle was always sneezing and puffy from allergies because he doesn't like to tell her no. Anyways, I have no choice but to invite her. My cousins are also invited. My crazy aunt asked why I didn't have any of my cousins standing up for our wedding, and I told her I already had plenty of bridesmaids and my fiance already chose his groomsmen. I feel bad that my mom is upset, but seriously, I'm almost 30 and this drama is so unnecessary. Can I just duct tape my aunt's mouth shut for the entire wedding and reception? That would really make my day that day.
Update: She didn't buy 2 Chippewas. That was supposed to say 3 Chiuauas. The little dogs with the bulgy eyes.
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